1. Field of the Invention
The present invention relates to the conversion of coal into liquid hydrocarbon products by reacting hydrogen with coal in the presence of a hydrogen-donor-solvent. More particularly, the present invention relates to the catalytic hydrotreatment of coal and coal liquids to effect removal of metals and heteroatoms.
2. Description of the Prior Art
Solvent extraction processes for converting coal to clean liquid or solid fuels generally comprise the following steps:
(1) coal extraction;
(2) separation of extract from undissolved residue; and
(3) hydrogenation of the separated extract.
In the coal extraction step, coal is slurried in an organic solvent and heated, often in the presence of added molecular hydrogen, to a temperature sufficient to dissolve or liquefy most of the organic material in the coal. A wide variety of solvents are known in the art, including hydrogen donor solvents, non-hydrogen donor solvents, and mixtures thereof. The solvent employed may be obtained from a previous conversion of coal or may be a solvent generated externally of the solvent extraction process or may be mixtures thereof. Thus, the solvent may be the liquid wherein the liquid product obtained by solvent extraction is dissolved, as well as the liquid in which the undissolved solids from the coal extraction are dispersed.
After extraction, solids that are present may be removed from the product stream. The product stream, separated from undissolved residue, may then be stripped of solvent and the solvent recycled to the extraction step. The remaining extract, which will hereinafter be referred to as "solvent-refined coal," is a solid at room temperature and contains very little (generally less than 10 weight percent) material boiling below 850.degree. F. The solvent-refined coal (which may still contain some "solvent") may thereafter be subjected to distillation to obtain products of various boiling ranges, some of which are useful as fuels. These fractions may then be further treated by refining processes, including coking, hydrogenation, cracking, hydrocracking, hydrotreating, and the like.
Alternatively, the product stream containing the solvent refined coal may be subjected to further treatment without first removing the solvent. It is known that such processing schemes have the advantage of treating an easier-to-handle material than those in which the solvent is separated before further treatment. Again, the mixture containing solvent-refined coal may be further treated by fractionation, coking, hydrogenation, cracking, hydrocracking, and the like.
A wide variety of materials have been suggested as suitable catalysts for coal liquefaction, coal liquefaction upgrading, and coal liquefaction solvent rehydrogenation. It is known that any conventional type of catalyst commonly used for hydrogenation of coal extract may catalyze desirable reactions in the first coal liquefaction zone. Moreover, since coal liquefaction catalysts are rapidly deactivated, employment of inexpensive hydrogenation catalysts which are only sufficiently active to accomplish the conversion of benzene insoluble extract to benzene solubles is desirable. For example, inexpensive, low-activity catalysts which have been suggested for coal liquefaction and initial catalytic upgrading of coal liquefaction products include spent catalysts from subsequent coal liquid treatment steps. U.S. Pat. No. 3,162,594 at column 8, lines 10-25 suggests that deactivated catalysts from a coal liquefaction product catalytic hydrocracking zone is a desirable coal liquefaction zone catalyst. Known coal liquefaction product hydrocracking catalysts are supported metals of Subgroups V-VIII of the Periodic Table. U.S. Pat. No. 3,232,861 suggests contacting deashed coal extract in a "prehydrocracking zone" with abraded catalyst fines recovered from a subsequent hydrocracking zone. See also U.S. Pat. No. 3,488,279.
In coal dissolution by liquefaction hydrogen donor techniques and in mild upgrading of the initially formed products to produce an acceptable boiler fuel or feedstock for further upgrading, there is a need for novel and inexpensive catalysts. An object of the present invention is an economically attractive catalytic process for the liquefaction of coal in a hydrogen donor solvent and for the mild upgrading of the initially formed product. A related object is an inexpensive, disposable material which catalyzes hydrogen interchange and metals and heteroatom removal in solvent extraction processes for the conversion of coal to more valuable hydrocarbon materials.